qpdf/TODO

2.1
===

 * Update documentation to reflect new command line flags and any
   other relevant changes.  Should read through ChangeLog and the
   manual before releasing 2.1.

 * Update release documentation to remember not to include debugging
   in the Windows release and to strip the DLL and executables.
   Consider making the "install" target do something useful for
   Windows.  Update README.windows in this case including taking out
   the mention of strip since it should be handled by the install
   step.  Determine whether -g with strip is different from not -g
   with strip.

 * Add comments for the security functions that map them back to the
   items in Adobe's products.

 * Have force version at least turn off object streams and maybe
   change security settings?

 * Add error codes to QPDFException.  Change the error interface so
   that warnings and errors are pointers that can be queried using
   more C API functions.  We need a way to get a full string as well
   as an error code, file name, offset, and message.  We should go
   through all error messages to try to include all these fields as
   appropriate.  Make sure invalid password is specifically
   detectable.  I/O errors and so forth should also be
   distinguishable.  Make sure all errors include information about
   the most recent read location including byte offset and
   object/generation number.

 * It might be nice to be able to trap I/O errors separately from
   other errors; especially be able to separate errors that the user
   can fix (like permission errors) from errors that they probably
   can't fix like corrupted PDF files, unsupported filters, or
   internal errors.  However, only QPDF::processFile(), which does the
   initial read, and QPDFWriter::QPDFWriter(), which does the initial
   write, are at all likely to generate such errors for a case other
   than a catastrophic failure.

 * "Delphi wrapper unit 'qpdf.pas' created by Zarko Gajic
   (http://delphi.about.com). .. use at your own risk and for whatever
   the purpose you want .. no support provided. Sample code provided."

2.2
===

 * Add ability to create new streams or replace stream data.  Consider
   stream data sources to include a file and offset, a buffer, or a
   some kind of callback mechanism.  Find messages exchanged with
   Stefan Heinsen <stefan.heinsen@gmx.de> in August, 2009.  He seems
   to like to send encrypted mail.  (key 01FCC336)

 * See whether we can do anything with /V > 3 in the encryption
   dictionary.  (V = 4 is Crypt Filters.)  See
   ~/Q/pdf-collection/R4-encrypt-PDF_Inside_and_Out.pdf

   Search for XXX in the code.  Implementation has been started.

   Algorithms from PDF Spec in QPDF_encrypt.cc have been updated.  We
   can at least properly verify the user password with an R4 file.  In
   order to finish the job, we need an aes-128-cbc implementation.
   Then we can fill in the gaps for the aes pipeline and actually run
   the test suite.  The pipeline may be able to hard-code the
   initialization vector stuff by taking the first block of input and
   by writing a random block for output.  The padding is already in
   the code, but the initialization vector is not since I accidentally
   started using an aes256 implementation instead of aes128-cbc.

 * Look at page splitting.


General
=======

 * The second xref stream for linearized files has to be padded only
   because we need file_size as computed in pass 1 to be accurate.  If
   we were not allowing writing to a pipe, we could seek back to the
   beginning and fill in the value of /L in the linearization
   dictionary as an optimization to alleviate the need for this
   padding.  Doing so would require us to pad the /L value
   individually and also to save the file descriptor and determine
   whether it's seekable.  This is probably not worth bothering with.

 * The whole xref handling code in the QPDF object allows the same
   object with more than one generation to coexist, but a lot of logic
   assumes this isn't the case.  Anything that creates mappings only
   with the object number and not the generation is this way,
   including most of the interaction between QPDFWriter and QPDF.  If
   we wanted to allow the same object with more than one generation to
   coexist, which I'm not sure is allowed, we could fix this by
   changing xref_table.  Alternatively, we could detect and disallow
   that case.  In fact, it appears that Adobe reader and other PDF
   viewing software silently ignores objects of this type, so this is
   probably not a big deal.

 * Pl_PNGFilter is only partially implemented.  If we ever decoded
   images, we'd have to finish implementing it along with the other
   filter decode parameters and types.  For just handling xref
   streams, there's really no need as it wouldn't make sense to use
   any kind of predictor other than 12 (PNG UP filter).

 * If we ever want to have check mode check the integrity of the free
   list, this can be done by looking at the code from prior to the
   object stream support of 4/5/2008.  It's in an if (0) block and
   there's a comment about it.  There's also something about it in
   qpdf.test -- search for "free table".  On the other hand, the value
   of doing this seems very low since no viewer seems to care, so it's
   probably not worth it.

 * Embedded files streams: figure out why running qpdf over the pdf
   1.7 spec results in a file that crashes acrobat reader when you try
   to save nested documents.

 * QPDFObjectHandle::getPageImages() doesn't notice images in
   inherited resource dictionaries.  See comments in that function.

 * Based on an idea suggested by user "Atom Smasher", consider
   providing some mechanism to recover earlier versions of a file
   embedded prior to appended sections.

Splitting by Pages
==================

Although qpdf does not currently support splitting a file into pages,
the work done for linearization covers almost all the work.  To do
page splitting.  If this functionality is needed, study
obj_user_to_objects and object_to_obj_users created in
QPDF_optimization for ideas.  It's quite possible that the information
computed by calculateLinearizationData is actually sufficient to do
page splitting in many circumstances.  That code knows which objects
are used by which pages, though it doesn't do anything page-specific
with outlines, thumbnails, page labels, or anything else.

Another approach would be to traverse only pages that are being output
taking care not to traverse into the pages tree, and then to fabricate
a new pages tree.

Either way, care must be taken to handle other things such as
outlines, page labels, thumbnails, threads, zones, etc. in a sensible
way.  This may include simply omitting information other than page
content.